An evaporator may be used in various systems, including a vapor compression chiller system whose primary components include a compressor, a condenser, an expansion device and the evaporator. The main components of the chiller system are interconnected to create a conventional closed-loop refrigeration circuit.
In basic operation of a vapor compression chiller system, the compressor discharges compressed gaseous refrigerant through a discharge line to the condenser, in which a cooling fluid cools and condenses the refrigerant. The condensed refrigerant is transferred from the condenser to the expansion device, wherein the refrigerant cools by expansion before entering an evaporator inlet of the evaporator as a two-phase mixture of liquid and vapor refrigerant. The two phase refrigerant mixture is distributed across a tube bundle provided within a shell of the evaporator. The refrigerant flows between the tubes, and in passing across the exterior of the tubes of the tube bundle, cools a heat absorbing fluid, which passes through the interior of the tubes of the tube bundle. The heat absorbing fluid is typically water or a water/glycol mixture. For the purposes of present discussion, the fluid is assumed to be water. The chilled water can then be pumped to remote locations for various cooling purposes.
The chilled water vaporizes the liquid portion of the refrigerant mixture that passes through and across the tube bundle. The vapor refrigerant is drawn by pressure differential toward a suction inlet or an evaporator outlet attached to the evaporator shell. Baffles in the evaporator help insure that primarily only the vapor portion of the refrigerant is conveyed to the suction inlet of the suction tube. From the suction tube, a suction line or pipe conveys vapor refrigerant to an inlet of the compressor so that the compressor can recompress the refrigerant to perpetuate the refrigerant cycle.
Liquid refrigerant remaining within the evaporator shell pools in the bottom of the evaporator. The liquid refrigerant is brought into heat exchange with the portion of the tube bundle that is immersed in the liquid. A pump or some other conventional means can return the liquid to any appropriate inlet associated with the evaporator.
Typical evaporators used in a chiller system have a suction baffle near the inlet of the suction tube. A function of the suction baffle in an evaporator is to minimize the carryover of liquid refrigerant into the suction tube or line during chiller operation. Due to design constraints, the suction inlet and suction tube in conventional evaporators are attached near the top of the evaporator, generally directly above the suction baffle, increasing the height of the evaporator.
Typical evaporator designs also include a region between the tube bundle and the suction baffle for refrigerant droplets to separate from the vapor flow. This region, termed droplet drop-out region, is also designed to minimize the amount of liquid refrigerant entering the suction tube.
A problem exhibited by evaporators of small size and capacity is that the inlet of the suction tube is relatively large and would intrude into the space below the suction baffle or droplet drop-out region if located too far from the top. In evaporators of small size and capacity, if the inlet of the suction tube intrudes into the space below the suction baffle, the effectiveness of the suction baffle is reduced or eliminated because a direct path is provided for the refrigerant to flow into the suction tube inlet resulting in carry-over of liquid into the suction tube. In this problematic design, the suction tube inlet bypasses the suction baffle, allowing a combination of liquid and vapor refrigerant to enter the suction tube or line to the compressor, thereby reducing the overall efficiency of the refrigerant system and risking damage to the compressor. Design principles used in evaporator design constrain suction baffle design and make it difficult to avoid the protrusion of the suction tube inlet into the vapor space below the suction baffle, especially for small capacity evaporators.
Therefore, what is needed is an evaporator design that prevents direct vapor refrigerant flow into the suction tube inlet and allows for horizontal or tangential placement of the suction tube. Another need is an evaporator design that allows for the suction tube inlet to be located partially below the suction baffle in the droplet drop-out region, thereby allowing for a more compact evaporator design and a more efficient refrigeration system.